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9 May – working on those pits

Late in the evening of 9 May, I spent about an hour and a half working on the mirror, with maybe 45 minutes actual grinding. Two wets with #320 carbo, tool on top, 1/3 diametral strokes, very light pressure. Rinse and dry the mirror, inspect, do another two wets. The giant megapit near the centre is visibly reducing (I can see the irregular bottom now – it looks like two overlapping pits. Eventually they’ll separate into two small pits, and shortly afterwards vanish completely), but a lot of brand new pits are appearing. I reckon this is good news, and I will continue for as long as necessary to try eliminate subsurface fracturing from previous grits. I suspect that I’ve learned more about grinding technique from dealing with the subsurface fracturing than any other experience so far. We’ll see if what I’ve learned is actually right on my next mirror!

I think that I am nearing the end with this grit, but am determined not to rush it. The real factor now is my inability to find more than an hour each week to work, rather than the speed at which glass is being removed. When I started I was hoping to be done in time for ScopeX, and I think that if I had no other projects running then I could easily have achieved that. Still… I have a more realistic understanding of my time now. This telescope will be built by Christmas, right in the middle of the rainy season, so first light might only be in 2012, but that’s okay. I’ve got more than enough going on to distract me if I start to feel impatient!

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Allen is an amateur astronomer, an IT professional, a podcaster, a father of five beautiful kids and a barely competent chess player.
He is also the director of the Astrophotography Section of the Astronomical Society of South Africa, where he coordinates and promotes the activities of people who are far better photographers than him.